Had this conversation last night. It depends upon the a/c weight.
Tab data in 5,000' increments below FL 290, 2000' increments above FL 290 -
777 @ 620,000 lbs? 10,000' 21,000' below OPT ALT
@ 600,000 lbs? 15,000' 17,000' below OPT ALT
@ 500,000 lbs? 25,000' 11,000' below OPT ALT
@ 460,000 lbs? 31,000' (MLW) 7,000' below OPT ALT
@ 400,000 lbs? 31,000' 10,000' below OPT ALT